1. Field of the Invention
The present invention relates to an ink-jet head and an ink-jet recording apparatus for discharging ink onto a recording medium to be recorded thereon.
2. Description of the Prior Art
An ink-jet recording apparatus for recording characters and images on a recording medium by using an ink-jet head having a plurality of nozzles for discharging ink has been conventionally known.
An outline of the ink-jet recording apparatus will be described below. FIG. 1 is a schematic diagram of the ink-jet recording apparatus which includes a pressure buffer. The ink-jet recording apparatus includes at least ink supply means 30 for supplying ink, an ink-jet head 20 for discharging ink, an ink supply path 50 which is a path for supplying ink from the ink supply means 30 to the ink-jet head 20, a pressure buffer 10 provided in the ink supply path 50 in the vicinity of the ink-jet head 20, and a carriage 40 which includes the ink-jet head 20 and the pressure buffer 10 that are mounted therein.
The ink-jet recording apparatus performs printing in such a manner that the carriage 40 which includes the ink-jet head 20 mounted therein reciprocates on a recording medium. The arrow of FIG. 1 indicates the reciprocation of the carriage 40 on the recording medium. In the case of performing printing, when the carriage 40 is accelerated or decelerated, a pressure fluctuation is generated inside the ink-jet head 20 due to an inertia of ink provided in the ink supply path 50 which is filled with the ink. The pressure fluctuation causes deterioration in image quality in the case of recording characters or images on a recording medium, and further causes a discharge failure. For this reason, it is necessary to provide the pressure buffer 10 in the ink supply path 50, which connects the ink supply means 30 and the ink-jet head 20 to each other, in the vicinity of the ink-jet head 20 so that the pressure fluctuation can be suppressed as much as possible.
Here, an example of the conventional pressure buffer 10 will be described. FIG. 2 shows a state where the pressure buffer 10 and the ink-jet head 20 according to the prior art are connected to each other, that is, a structure of the carriage 40 of FIG. 1. Note that the arrow X of FIG. 2 indicates a gravity direction. In other words, a lower side of FIG. 2 indicated by the arrow X indicates a ground side. FIG. 3 is a cross-sectional diagram of the pressure buffer 10 of FIG. 2 taken along the line f-f′.
In FIG. 3, a main body 112 of the pressure buffer 10 has a concave portion 114 on at least one surface thereof, and a flexible film 111 is applied to the concave portion 114 so as to hermetically seal the concave portion, to thereby form a chamber 103. As shown in FIG. 2, the chamber 103 has at least an ink flow inlet 102 through which the ink flows into the chamber 103 from the ink supply means 30, and an opening portion 101 for supplying the ink to the ink-jet head 20. The chamber 103 is filled with the ink so as to prevent air bubbles which cause the discharge failure of the ink, from being contained in the chamber 103, so as to fill the ink through pressurization, and so as to obtain a stable characteristic to buffer pressure. The pressure buffer 10 described above is disclosed in JP 2005-14315 A.
Next, problems to be solved by the present invention will be described below.
In the structure according to the prior art, as shown in FIG. 2, the opening portion 101 of the pressure buffer 10 is provided at an uppermost portion of the pressure buffer 10. Accordingly, in order to connect the ink-jet head 20 to the pressure buffer 10 to each other, it is necessary to separately provide an ink supply path 105 such as a tube, between the opening portion 101 and the ink-jet head 20, outside the pressure buffer 10. As a result, there arise problems in that the number of components is increased, and manufacturing costs are increased. In addition, in a case of arranging the ink-jet head 20 and the pressure buffer 10 to be closer to each other, for example, it is necessary to separately provide a tube or the like. As a result, there arises a problem in that a peripheral space cannot be effectively used.
Further, there arises another problem in that, when vibration in the vertical direction is applied to the carriage 40, a space formed between positions indicated by a-a′, that is, space between an uppermost position of the ink supply path 105 and a lowermost position of a nozzle 106 of the ink-jet head 20 becomes a space which is confined a pressure. As a result, the pressure fluctuation is generated due to the inertia of the ink provided in the space between the positions indicated by a-a′ which is filled with the ink 113. Therefore, there arise problems in that the pressure fluctuation causes a meniscus 104 to be displaced in a positive or negative direction, and a volume of ink droplets to be discharged, or a discharge rate is modulated, which leads to density unevenness.